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In 1973, the IBM 3340 disk storage unit, often known by its internal project name “Winchester,” became the industry disk storage standard through the decade. The 3340 featured a small, light read–write head and a design that enabled the head to ride close to the disk surface on an air gap that was 18 millionths of an inch thick. At the time, the 3340 doubled the information density of IBM disks to nearly 1.7 million bits per square inch. The low-cost head–slider structure of the Winchester disk made it possible to use two heads per surface. The disk, the disk spindle and bearings, the carriage, and the head–arm assemblies were incorporated into a removable sealed cartridge called the IBM 3348 Data Module.
Since the rapid introduction of the IBM RAMAC 305 in 1956, disk facilities have been crucial to the rapid evolution of computer systems. On a historical note, customer-removable and interchangeable disk packs were introduced as a feature of the IBM 1311 in 1962. The 1974 Journal paper featured here describes the design of the IBM 3340, which required the development of the aforementioned special magnetic read–write heads. In particular, the heads used a tri-rail, low-mass air-bearing slider. The authors also discuss a method of improving data integrity, utilizing a “disk-defect skipping” procedure.
In 1973, the task of increasing performance while lowering the cost per unit of storage was particularly challenging in small and intermediate-sized disk drives. Although the number of heads and disks might be reduced, the cost of servo controls, power supplies, and motors did not diminish in proportion to the reduction of data capacity. The IBM 3340 was developed, in part, to address this problem.
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